test=penguinBinStack

[Fil]

A tiny step (and test) for bin + stack.

I'm sending this very much half-baked, in case it helps (won't have more time today).

[Fil]

[mbostock]

This is helpful, thanks. I want to try a slightly different approach — the bin transform is already computing the z channel, so it should be able to return the materialized channel (using lazyChannel like the stack transform), such that if you pass fill: "species" to the bin transform, it’ll use it for z and make it available for rendering the bins, rather than needing a fill: "z" which is computed after the bin transform is applied.

[Fil]

Just to complete the comments on this draft and examples:

• The 1-d examples were a bit awkward since stackX needs to be given a specific y (location) to stack on. The location I've chosen is y:x0 (it could also be y:x1 with no incidence—it just needs to be an identifier allowing to group the bins that have the same (x0, x1) with different z). There's probably some possibility of improvement here.

• The 2-d example doesn't allow to specify fill: "species", since only z is passed. I won't look into it but this is a desirable feature.